1. Field of the Invention:
The present invention relates to a constant-velocity driving arrangement for a camera shutter of the type in which a sector is driven by a motor.
2. Description of the Prior Art:
Camera shutters capable of performing many various exposure modes by driving a sector with a motor are put to practical use. Since a battery is used as a motor driving power supply, the speed of travel of the sector tends to change due to variations in the battery voltage, resulting in errors in the amount of exposure.
Shutter devices of the type in which a sector is driven by a motor are widely used in camera electronically controlled. Such a shutter device can perform many various exposure modes, but is problematic in that the exposure accuracy is poor since the rotational speed of the motor depends on the voltage of a battery which is a source of drive energy for the shutter device. To solve the above problem, it has been customary to provide a higher battery voltage setting than the rated voltage of the motor, and to supply a constant voltage to the motor through a constant-voltage circuit that utilizes the conduction resistance of a transistor. However, when the voltage of the battery is high, the drive voltage is lowered by the constant-voltage circuit, and hence the battery power is consumed as Joule heat resulting in a shortened battery service life, and an excessive margin is required for the power supply voltage.